backend-drm: add support for blend mode plane property

This is used in the next commits.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>

libweston/backend-drm/drm-internal.h

@@ -461,6 +461,8 @@ struct drm_plane_state {
 	uint64_t zpos;
 	uint16_t alpha;
 
+	enum wdrm_plane_blend blend_mode;
+
 	enum wdrm_plane_color_encoding color_encoding;
 	enum wdrm_plane_color_range color_range;
 
@@ -1041,6 +1043,10 @@ bool
 drm_plane_supports_color_range(struct drm_plane *plane,
 			       enum wdrm_plane_color_range range);
 
+bool
+drm_plane_supports_blend_mode(struct drm_plane *plane,
+			      enum wdrm_plane_blend blend_mode);
+
 void
 drm_output_render(struct drm_output_state *state);
 

libweston/backend-drm/drm-kms-enums.h

@@ -56,6 +56,7 @@ enum wdrm_plane_property {
 	WDRM_PLANE_ZPOS,
 	WDRM_PLANE_ROTATION,
 	WDRM_PLANE_ALPHA,
+	WDRM_PLANE_BLEND,
 	WDRM_PLANE_COLOR_ENCODING,
 	WDRM_PLANE_COLOR_PIPELINE,
 	WDRM_PLANE_COLOR_RANGE,
@@ -179,6 +180,17 @@ enum wdrm_colorop_lut3d_interpolation {
 	WDRM_COLOROP_LUT3D_INTERPOLATION__COUNT,
 };
 
+/**
+ * Possible values for the WDRM_PLANE_BLEND property.
+ */
+enum wdrm_plane_blend {
+	WDRM_PLANE_BLEND_NONE = 0,
+	WDRM_PLANE_BLEND_PREMULT,
+	WDRM_PLANE_BLEND_COVERAGE,
+	WDRM_PLANE_BLEND__COUNT
+};
+#define WDRM_PLANE_BLEND_DEFAULT WDRM_PLANE_BLEND_PREMULT
+
 /**
  * List of properties attached to a DRM connector
  */

libweston/backend-drm/kms.c

@@ -109,6 +109,18 @@ struct drm_property_enum_info plane_color_range_enums[] = {
 	},
 };
 
+struct drm_property_enum_info plane_blend_enums[] = {
+	[WDRM_PLANE_BLEND_NONE] = {
+		.name = "None",
+	},
+	[WDRM_PLANE_BLEND_PREMULT] = {
+		.name = "Pre-multiplied",
+	},
+	[WDRM_PLANE_BLEND_COVERAGE] = {
+		.name = "Coverage",
+	},
+};
+
 const struct drm_property_info plane_props[] = {
 	[WDRM_PLANE_TYPE] = {
 		.name = "type",
@@ -135,6 +147,11 @@ const struct drm_property_info plane_props[] = {
 		.num_enum_values = WDRM_PLANE_ROTATION__COUNT,
 	},
 	[WDRM_PLANE_ALPHA] = { .name = "alpha" },
+	[WDRM_PLANE_BLEND] = {
+		.name = "pixel blend mode",
+		.enum_values = plane_blend_enums,
+		.num_enum_values = WDRM_PLANE_BLEND__COUNT,
+	},
 	[WDRM_PLANE_COLOR_ENCODING] = {
 		.name = "COLOR_ENCODING",
 		.enum_values = plane_color_encoding_enums,
@@ -815,6 +832,31 @@ drm_plane_supports_color_range(struct drm_plane *plane,
 	return enum_info->valid;
 }
 
+/**
+ * Check if a blend mode is supported by a KMS plane
+ *
+ * If the blend mode property is not supported by the plane, this assumes that
+ * the blend mode is unsupported if different from WDRM_PLANE_BLEND_DEFAULT.
+ *
+ * @param plane The KMS plane
+ * @param blend_mode The blend mode to check
+ * @return True if supported, false otherwise
+ */
+bool
+drm_plane_supports_blend_mode(struct drm_plane *plane,
+			      enum wdrm_plane_blend blend_mode)
+{
+	const struct drm_property_info *info = &plane->props[WDRM_PLANE_BLEND];
+	const struct drm_property_enum_info *enum_info;
+
+	if (info->prop_id == 0)
+		return blend_mode == WDRM_PLANE_BLEND_DEFAULT;
+
+	enum_info = &info->enum_values[blend_mode];
+
+	return enum_info->valid;
+}
+
 /**
  * Mark an output state as current on the output, i.e. it has been
  * submitted to the kernel. The mode argument determines whether this
@@ -1603,6 +1645,28 @@ drm_plane_set_color_range(struct drm_plane *plane,
 				   color_range);
 }
 
+static int
+drm_plane_set_blend_mode(struct drm_plane *plane,
+			 enum wdrm_plane_blend blend_mode,
+			 drmModeAtomicReq *req)
+{
+	struct weston_compositor *wc = plane->base.compositor;
+
+	weston_assert_s32_ge(wc, blend_mode, 0);
+	weston_assert_s32_lt(wc, blend_mode, WDRM_PLANE_BLEND__COUNT);
+
+	if (plane->props[WDRM_PLANE_BLEND].prop_id == 0) {
+		if (blend_mode == WDRM_PLANE_BLEND_DEFAULT)
+			return 0;
+
+		return -1;
+	}
+
+	weston_assert_true(wc, drm_plane_supports_blend_mode(plane, blend_mode));
+
+	return plane_add_prop_enum(req, plane, WDRM_PLANE_BLEND, blend_mode);
+}
+
 static bool
 colorop_enforce(drmModeAtomicReq *req, const struct drm_colorop *colorop,
 		char **err_msg)
@@ -1952,6 +2016,10 @@ drm_output_apply_state_atomic(struct drm_output_state *state,
 					      WDRM_PLANE_ALPHA,
 					      plane_state->alpha);
 
+		ret |= drm_plane_set_blend_mode(plane,
+						plane_state->blend_mode,
+						req);
+
 		ret |= drm_plane_set_color_encoding(plane,
 						    plane_state->color_encoding,
 						    req);

libweston/backend-drm/state-helpers.c

@@ -59,6 +59,8 @@ drm_plane_state_alloc(struct drm_output_state *state_output,
 	state->alpha = (plane->alpha_max < DRM_PLANE_ALPHA_OPAQUE) ?
 		       plane->alpha_max : DRM_PLANE_ALPHA_OPAQUE;
 
+	state->blend_mode = WDRM_PLANE_BLEND_DEFAULT;
+
 	state->color_encoding = WDRM_PLANE_COLOR_ENCODING_DEFAULT;
 	state->color_range = WDRM_PLANE_COLOR_RANGE_DEFAULT;